The present invention relates generally to heat exchangers which utilize a plurality of tubes disposed therein and, more particularly, to tube sheet support mechanisms which provide radial support to a tube sheet and transfer forces radially from the tube sheet to an outer shell structure of the heat exchanger. More specifically, the present invention relates to a radial support mechanism which transfers radial forces to the outer shell of a steam generator which comprises two coaxially associated shells.
In nuclear power generating systems, heat exchangers are used generally to transfer heat from a radioactive fluid to a non-radioactive fluid which will eventually flow through a turbine. These two fluids are isolated from each other to prevent radioactive contamination of the turbine. This heat exchanger, when utilizing water as the heat transferring medium, is referred to as a steam generator and will be referred to as such herein. Typically, a steam generator of this kind is constructed with an outer shell structure which contains both the radioactive and non-radioactive fluids, each flowing through individual separate passageways. Within this outer shell, the steam generator is compartmentalized to provide a means for providing thermal communication between these fluids without permitting them to come into physical contact with one another. This can be accomplished by passing one of the fluids through a plurality of thermally conductive tubes while causing the other fluid to flow around and in contact with the outside surfaces of these tubes.
The above-mentioned heat exchanger tubes may be U-shaped in such a way as to connect, in fluid communication, two adjacent fluid compartments located at the same end of the heat exchanger, or, alternatively, the tubes may be straight and connect, in fluid communication, compartments located at opposite ends of the heat exchanger. In either case, the fluid flowing around the outside surfaces of the heat exchanger tubes can cause lateral movement and possibly severe vibration in those tubes. In order to provide lateral support for the heat exchanger tubes, which may be of significant length, tube support plates are disposed within the steam generator. These tube support plates generally are flat circular plates with a plurality of holes through their planar surfaces. The tubes of the heat exchanger are passed through these holes with a minimal clearance so that the lateral movement of the tubes is constrained by the tube support plate. It should be understood that the tube support plate is typically designed to provide no restriction on a tube's longitudinal movement through the plate but, only to provide support which prevents lateral movement radial to the tubes which would otherwise be caused by the rapid passage of fluid over their outside cylindrical surfaces.
In steam generators which utilize a two shell construction with the tube support plates being disposed inside the inner shell, it sometimes becomes necessary to radially support the tube support plates in a way that transfers radial forces to the outer shell because of its greater strength. Even in circumstances which do not require this transfer of radial forces to the outer shell, the inner shell must usually be strengthened in some manner in order to be able to withstand radial forces exerted by the tube support plate. In this latter case, the inner shell must be locally strengthened in the region where forces from the tube support plate can be encountered.
The present invention is particularly applicable to steam generators with this type of two-shell construction. It comprises a means for exerting a force between the inner of the two shells and the tube support plate in a direction radial to the inner shell. Also, it comprises means for exerting a force between the inner and outer shells. The combination of these two means, rigidly connected to each other, transfers radial forces from the tube support plate to the outer shell and avoids potential damage to the inner shell caused by these forces. These two portions of the present invention are in threaded association with each other in a way that enables them to adjust for varying radial distances between the outer cylindrical surface of the tube support plate and the inner cylindrical surface of the outer shell. This threaded association also enables the tube support plate to be centered in relation to the inner shell during initial construction. Once assembled, the segments of the present invention can be welded to each other and also to the inner shell in such a way as to result in its rigid attachment to the inner shell.
The present invention provides a means for radially supporting a tube support plate in a steam generator while transferring radial forces from the tube support plate directly to the outer shell while avoiding potential damage to the lower strength inner shell during periods when severe radial forces on the tube support plate are experienced.